In general, the invention relates to signalling between the transmitting and the receiving device in wireless telecommunication connections. In particular, the invention relates to how to transmit information in between the receiver and the transmitter as for the changes related to the processing of data to be transmitted over a wireless telecommunications connection, such as code division and channel coding. As an exemplary telecommunications connection, we shall deal with a radio connection between a mobile station and a base station in a third-generation digital cellular radio system.
Many services designed for new wireless telecommunications systems require that the part of the data transmission capacity represented by the radio interface that is reserved for the telecommunications connection transmitting the service can be used in a flexible manner, for example by increasing or reducing channel coding, which affects the user data bitrate achieved in said connection: the more channel coding is used, the slower is the transmission rate of the data proper to be transmitted, and vice versa. The need for changing the channel coding, code division or other such factor used by the transmitter is generally due to the fact that a certain rate of accuracy is attempted to be maintained in the connection irrespective of the changing conditions of the proceeding radio waves. In a system where the data to be transmitted in between the transmitter and the receiver is arranged in frames, each frame may, in an extreme case, contain data that is processed in a different way than in the preceding or the successive frame. In one way or another, the transmitter and the receiver must find mutual understanding as to how the data to be transmitted in each frame has been processed in the transmitter, and consequently how it should be processed in the receiver.
FIG. 1 illustrates a typical prior art frame 100, which is the basic unit of data to be transmitted over a radio interface. In general, the frame includes certain header parts, a certain number of data to be transmitted and a check code for checking the faultlessness of the frame. The header parts can be transmitted through a different logic channel than the data proper. In FIG. 1, among the frame header parts there is particularly illustrated the FCH (Frame Control Header) field 101, containing a given number of bits, for instance 6 or 12 bits. The FCH field can be transmitted for example through a given control channel (DPCCH; Dedicated Physical Control Channel), and the data to be transmitted connected to said frame can be communicated through a data channel (DPDCH; Dedicated Physical Data Channel). The FCH field bits must, among other things, transmit information as to what kind of channel coding, spreading and/or other data processing method has been used in processing the transmittable data connected to the frame in question. In a CDMA (Code Division Multiple Access) system, the FCH field may indicate for instance the value of the processing gain that has been used in connection with the spreading of the data channel.
In prior art frames, the length of the header part is generally attempted to be kept as short as possible in order to be able to use as large a share as possible of the frame for transmitting the data proper. This unavoidably results in that the number of data processing options that can be indicated by means of the FCH field bits illustrated in FIG. 1 is limited. In particular this drawback becomes apparent in situations where in between the transmitter and the receiver, there are several simultaneous but logically separate connections, where the code division or channel coding or other factor connected to data processing may change irrespective or the rest, and where the information related to said connections must be transmitted in the common header field. By means of the FCH field bits, or bits of a corresponding field reserved for this purpose, it should now be possible to indicate a large number of different combinations of data processing options.
A natural alternative for solving the above mentioned problem is to increase the number of bits in the FCH field or in a corresponding field reserved for this purpose. However, it should be noted that it is by no means necessary in all connections to have a large number of different code division options or other data processing connected factors or combinations thereof In a connection where the need of FCH field bits is low, a large number of bits would unnecessarily reduce the relative space reserved for the data to be transmitted and load the system, because the system would try to transmit fully unnecessary bits without transmission errors from transmitter to receiver.
The object of the present invention is to introduce a method and system whereby the problem caused by the number of bits in the above mentioned FCH field or a corresponding field reserved for this purpose can be eliminated.
The invention relates to a method for indicating the actions performed in the processing of the data to be transmitted in a telecommunications system where the transmittable data is arranged in frames and where, in order to process said data, a number of mutually optional actions are available. The method according to the invention comprises a phase where
the transmitting device includes in the frame to be transmitted a predetermined number of control bits, and the value of said bits indicates how the transmittable data contained in the frame should be processed prior to transmitting.
The method according to the invention is characterized in that in addition to what was said above,
there is defined how many mutually optional actions are available for processing the data to be transmitted,
there is defined the number of control bits in the frame, so that the number of actions indicated with the allowed control bit values is at least as high as the number of available, mutually optional actions, and
in the frame to be transmitted, there is included a defined number of control bits.
In addition to this, the invention relates to an apparatus for realizing data transmission in a telecommunications system like the one described above. The apparatus according to the invention is characterized in that it comprises means
for defining how many mutually optional actions are available for processing the data to be transmitted, and
for defining the number of control bits in the frame, so that the number of actions indicated with the allowed control bit values is at least as high as the number of available, mutually optional actions.
In signalling in between the transmitter and the receiver, an exactly correct number of bits is arranged for indicating spreading, channel coding and other corresponding factors connected to data processing, when the bit quantity is not fixed in advance, but the number and allocation of said bits for indicating different factors may vary. In between the transmitter and the receiver, there is provided a mechanism whereby both devices obtain information as to how many bits are used for indicating the factors connected to data processing, and how they are allocated.
One possibility for sending information of the number and allocation of bits to the transmitter and the receiver is to define a certain message to be exchanged between the transmitter and the receiver, said message indicating the existing number and allocation of bits. Another possibility is to establish an unequivocal correspondence between some higher-order concept, such as the QoS, Quality of Service required of the bearer service, or a contributing factor thereof, and the number and allocation of bits. In that case the number and allocation of bits does not have to be separately indicated, but both the transmitting and the receiving device can compute this information as soon as the higher-order concept in question has been agreed upon.